Device comprising an electric discharge tube of the electron-beam type



July 10, 1956 A. J. w. M. VAN'OVERBEEK ETAL 2,754,375

DEVICE COMPRISING AN ELECTRIC DISCHARGE TUBE OF THE ELECTRON-BEAM TYPEFiled June so, 1951 INVENTORS I A N w MARE von ADRIANUS JOH N ES ILHEOERBEEK JOHANN LODEWIJK HENDRIK JONKER DEVICE COMPRISING AN ELECTRICDISCHARGE TUBE OF THE ELECTRON-BEAM TYPE Adrianus Johannes WilhelmusMarie Van Overbeek and Johan Lodewiik Hendrik .lonker, Eindhoven,Netherlands, assignors to Hartford National Bank and Trust Company,Hartford, Conn., as trustee Application June 30, 1951, Serial No.234,484

Claims priority, application Netherlands July 13, 1950 2 Claims. (Cl.179-171) This invention relates to devices comprising an electricdischarge tube of the electron-beam type, with the use of which a veryhigh mutual conductance can be achieved in a simple manner.

It has previously been suggested to increase the deflection-sensitivityof a tube of the deflected-beam type by means of a space chargedeveloped between the beam and the deflection electrode, the deflectiondue to the deflection electrode being assisted by the space charge. Theobject here was an improvement in the deflection control itself in atube having a double control. In addition, according to the presentinvention it has been found possible to utilise the influence of spacecharge effects to achieve a very high mutual conductance, even in thecase of intensity control, if the electrons are directed to any one ofthe collecting electrodes only as a result of space charges which areformed by the beam current itself and are in accordance with theintensity control of the beam current. The deflection, or actuallydispersion, of the electron paths due to these space charges, whichdeflection is generally considered undesirable in intensity-control beamtubes, is thus used to direct the electrons normally travelling to agiven collecting electrode on to a further collecting electrode. Thelastrnentioned collecting-electrode will generally be the outputelectrode (anode). When the intensity of the beam current is increasedby the action of the control electrode an increasing current flows tothe collecting electrode (anode) and this increased flow is enhancedbecause,

simultaneously with the increase of the beam current,

the beam is directed to this electrode to a greater extent. The beam isthus deflected, fully in accordance with the intensity control of thebeam current, without any provision for a separate deflection control.

This mode of operation, i. e., deflection added to intensity-control asa result of space-charge effects, is achieved with advantageous resultsin the device according to the invention comprising an electricdischarge tube of the electron-beam type which includes at least acathode, an intensity-control electrode and two collecting elec trodesand in which the electrons can be directed on to any one of thecollecting electrodes by space charges formed by the beam itself inaccordance with the intensity control of the beam current, the tubeexhibiting during operation a straight beam which, at a given lowcurrent strength, travels completely through an aperture in onecollecting electrode of disc shape but, as a result of the dispersionbrought about by space charges occurring in the axis of the beam,largely reaches the said disc-shaped collecting electrode in the case ofsufficiently-high current strength.

The current control-grid voltage characteristic of this electrodeconsequently has a very high mutual conductance, which may be increasedby forming this electrode as a secondary emission auxiliary cathode.

In order that the invention may be more clearly understood and readilycarried into eflect, it will now be deatent scribed more fully withreference to the accompanying drawing, in which Fig. 1 showsdiagrammatically one embodiment of a tube suitable for use in a deviceaccording to the invention, and

Fig. 2 shows the IaVg characteristic curve of such a tube.

Referring to Fig. l, the cathode is designated 1 and the intensitycontrol electrode 2. A screen grid is shown at 3. The control electrode2 may itself comprise small screens so that the electron flow isconcentrated to form a beam but, as an alternative, separatebeam-forming electrodes may be provided. In either event a straight beamis formed which passes through an annular electrode 4, the space chargeelectrode, maintained at zero (ground) or at a low potential and which,in the case of a given low current strength, travels completely throughan aperture in a first disc-shaped collecting electrode 6 and reaches asecond collecting electrode 5. The first collecting electrode 6 ispreferably coated with secondaryemissive material and consequently actsas a secondaryemission auxiliary cathode. Owing to the presence of theelectrode 4, which may be separated, if desired, to form two spaced butelectrically interconnected electrodes, the development of a spacecharge within the electrode 4 and adjacent thereto in the axis of thebeam in the case of an increasing beam current is assisted, with theresult that the electron paths are deflected, i. e., the beamcrosssection is enlarged, and more and more electrons reach theauxiliary cathode or first collecting electrode 6 as the beam currentrises. The secondary electrons from this electrode 6 are collected by agrid-like output anode 7 which is connected to an output circuit 8.Since an increase in beam current arriving at the auxiliary cathode orfirst collecting electrode 6 is assisted by the dispersion of the beamdue to this current increase, a greatly increased mutual conductance isobtained.

Fig. 2 shows the Ia-Vg characteristic curve of a normal tube which hasintensity control but without the use of space charge dispersion (curve1). Curve II is the IaVg characteristic curve to the same scale of asimilar tube in which space charge dispersion is used. In order toprovide a true comparison between the two tubes, the current Ia is takenfrom an electrode 6 (Fig. l) which is not coated with a secondaryemitting substance. These curves clearly show the intense increase inmutual conductance, the advantage being that the latter is obtainablewithout the necessity of very accurate electrode machining or very smallelectrode spacings.

What we claim is:

l. A circuit arrangement comprising a tube having a high mutualconductance characteristic; said tube comprising a cathode, a controlelectrode, a screen grid, at first collecting electrode having anaperture therein for the passage of an electron beam therethrough andhaving a secondary-electron-emissive surface facing the cathode, asecond collecting electrode on the side of the first collectingelectrode remote from the cathode, a grid-like anode disposed adjacentthe secondary-electron-emissive surface of said first collectingelectrode in a position to receive electrons emitted therefrom, and aspace charge electrode disposed between the screen grid and saidgridlike anode and spaced therefrom and surrounding the beam ofelectrons; means to apply constant positive potentials with respect tosaid cathode to said grid-like anode and said second collectingelectrode, means to apply to said space charge electrode a constantpotential between zero and a positive amount which is small with respectto the potentials applied to the collecting electrodes whereby a portionof the electron beam alternately impinges upon the first and secondcollecting electrodes with high and low beam intensities, respectively,in accordance with the intensity of the beam, means for applying apositive in which the space charge electrode comprises a conpotential tosaid screen rid, mean' 'fd ap lying gm'input sinuous annular electrodethrough which the beam passes. signal to said control electrode to varythe intensity of References Cited in th file of this patent we beam Q eec n a d QutPu g m n lc i 2: ai

grid-like anode for deriving therefrom anamplified 'elc- 5 UNITED STATESPATENTS tricahsignal correspondingto the input signal applied to23394-3393 95 -t----v --t--- a 9 saidcontrolielectrede. 2 h v v253835160 f ay 1 1951 2. An electron discharge device as claimed in'claim -1 2,559,524 Thompson July 1951 2,563,482 Nelson Aug. 7,1951

